(1) Field of the Invention
The present invention relates to a fabrication method used for semiconductor devices, and more specifically to an improved process for polycide coating of contact holes in a dielectric layer.
(2) Description of Prior Art
The trend in the semiconductor industry to smaller, higher performance silicon devices, has been influenced by the ability of specific semiconductor disciplines to achieve micro-miniaturazation. Advances in photolithography, via more sophisticated exposure cameras, as well as development of more sensitive photoresist materials, have, allowed sub-micron images in photoresist materials to be routinely achieved. Comparable breakthroughs in the dry etching technology have allowed the sub-micron images in photoresist to be successfully transferred to underlying semiconductor materials via anisotropic reactive ion etching, (RIE), procedures. Other semiconductor fabrication disciplines, such as low pressure chemical vapor deposition, (LPCVD), and ion implantation, (I/I), have also contributed to the attainment of smaller, higher performing silicon devices.
However with the use of sub-micron feature, for specific elements of a semiconductor device, specific vulnerabilities, in terms of yield and reliability, arise. For example a device feature, needed to be reduced to successfully achieve micro-miniaturazation, is the contact or via hole, used to electrically connect; either two levels of wiring, or an active device region in silicon to an overlying wiring level. With the trend to sub-micron images, contact holes with diameters as small as 0.35 .mu.M have been used. The decreased contact hole diameter, although successful in allowing for the fabrication of smaller silicon chips, has put special demands on the properties of the materials used to fill these small openings. First the material has to inherently possess excellent current carrying capabilities. The excellent electromigration resistance of refractory metals, such as tungsten, and also silicides such as tungsten silicide, has made these materials leading candidates for contact hole filling. An area of concern is the inability of the refractory or silicide, to completely fill the contact, that is the filling process supply adequate step coverage. This becomes more imperative as the contact hole diameter decreases. A solution to the filling criteria is offered by Cleeves, et al, in U.S. Pat. No. 5,366,929, in which a selective fill is described using a sputter etch clean followed by a selective deposition. This solution although presenting possiblities of optimum fills, is complex and costly. Another area of concern with the use of refractory or silicide fills is the ability to achieve adhesion between the fill material and the contact hole materials. Many solutions have been offered, such as the use of titanium or titanium nitride films as adhesion layers, used to coat the contact hole prior to the fill deposition. Hasegawa, et al, in U.S. Pat. No. 5,374,591, offer a titanium nitride adhesion layer, followed by an etch back of the titanium nitride, at the edges of the contact, again directed at improving the subsequent fill process. Again, however this process is complex and costly. The fabrication process now described in this invention will offer an improved adhesion layer., as well as an optimized fill method enabling simple, reliable and non-costly contacts to be used.